How to get a head to track an empty
The following should work:

Add the empty to your scene and position it in front of the head, then select your head object and apply rotation by pressing CTRL+A and select "rotation" from the list:


Now with your head still selected, go to the constraints panel and add a "Track To" constraint, and in the Target field select the Empty you want the head to follow:


Note: You may have to change the axis in the Track To constraint, depending on which way your head is looking. Judging by your screenshot, I suspect it will be something like -Y